Generally, perfluorooxyalkylene group-containing compounds, hereinafter referred to “perfluoroether group-containing compounds”, have very small surface free energy, and, therefore, have water- and oil-repellency, a releasing property, and a stainproof property. The afore-mentioned compounds are widely used to utilize their properties as a commercial water- and oil-repellent, stainproof agent for paper and fiber, water- and oil-repellent, stainproof agent for display surfaces, and anti-oil agent for precision instruments.
It is known to use a silane in order to make a perfluoroether group adhere tightly to a substrate. For instance, patent literature 1 listed below discloses a fluoroaminosilane compound and patent literature 2 discloses an anti-reflection film whose stain-preventive layer contains the silane coupling agent represented by the following formula (7). However, the silane coupling agent has such problems that an amount of a hydrolysable group per molecule is insufficient; accordingly too much time is required for the agent to cure; and adhesion of the agent to a substrate is bad.
                wherein Rf2 is a linear or branched perfluoroalkyl group having 1 to 16 carbon atoms, R is an alkyl group having 1 to 10 carbon atoms, o is an integer of from 1 to 50, p is an integer of from 0 to 6, q is an integer of from 0 to 3, and r is an integer of from 0 to 3, provided that 0<p+q<=6.        
To solve the afore-mentioned problems, patent literature 3 discloses a silane coupling agent which has a perfluoropolyether group having two or more hydrolysable groups on its ends. The treating agent is good in adhesion to a substrate and provides a water- and oil-repellent surface where a slipping property is good and stain is easily wiped off.
For the requirements, “to make a surface stainproof” and “to make stain easily removed”, the afore-mentioned treating agent meets the former requirement by its water- and oil-repellency or low surface energy, and the latter requirement by its improved surface slipping property, respectively. However, recently, it is pointed out that stain such as fingerprint and sweat stands out as a white body and is more noticeable on surfaces of anti-reflection films, protecting films, and filters which have been surface treated with the afore-mentioned treating agent than on a surface which is not surface treated.
In order to make fat and oil stain less noticeable, it is known to treat a surface with a surface treating agent which comprises a hydrocarbon group, whereby the hydrocarbon group is exposed on the surface, then, the stain spreads on the surface and, therefore, the stain becomes less noticeable (patent literature 4). However, the treated surface becomes lipophilic and, therefore, the fat and oil stain adheres more easily to the surface and is more difficult to be removed than on an untreated surface.    [Patent literature 1] Japanese Patent Application Laid-Open No. Hei-11-29585    [Patent literature 2] Japanese Patent Application Laid-Open 2001-188102    [Patent literature 3] Japanese Patent Application Laid-Open 2007-197425    [Patent literature 4] Japanese Patent Application Laid-Open 2002-367229